Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry all produce. Trim and thinly slice scallions, separating whites from greens. Trim and peel carrots, then slice into 1/2-inch-thick pieces on a diagonal. Halve, peel, and thinly slice onion.

In a small bowl, combine sour cream, scallion whites, 1/2 tsp horseradish powder (we sent more), and 1 TBSP water. Season with salt.

In a small microwave-safe bowl, microwave 3 TBSP butter until softened, about 10 seconds. Stir in 1/2 tsp garlic powder (we sent more) and a pinch of salt. Halve baguettes, then toast in a toaster or toaster oven until lightly browned. Spread garlic butter onto toasts, then cut each half on a diagonal.

Toss carrots on a baking sheet with a drizzle of oil, salt, and pepper. Roast until browned and tender, about 20 minutes.

Pat steak dry with paper towels; season all over with salt and pepper. Heat a large drizzle of oil in a large pan over medium-high heat. Add steak and cook to desired doneness, 3-6 minutes per side. Turn off heat; remove from pan and set aside. Let rest at least 5 minutes before serving.

Heat another drizzle of oil in same pan over medium-high heat. Add onion, 1/2 tsp sugar, salt, and pepper. Cook, stirring, until softened, 3-5 minutes. Stir in stock concentrate and 2 TBSP water; simmer for 1 minute. Turn off heat. Stir in 1 TBSP butter. Divide steak, carrots, and garlic bread between plates. Top steak with onion. Garnish with scallion greens. Serve with horseradish cream on the side.